I will be in Medellin for one week in May (11th to 15th) and would like to set up some interviews with English language institutes for when I am there. I am finding it quite hard to find the contact details of institutes in Medellin on the web. Could anyone guide me to a relevant forum post or infomation portal where I might find contact details?

Also, do I need to have permission to find a contract in Colombia before I apply for my working visa? I am in Peru at the moment and here I require a permission to sign contract visa!

You could try Centro Colombo. And also International House is looking for people in Medellin at the moment, but the interviews are in Bogota. I've found the best bet is to call and arrange an interview. The yellow pages are your best option:

And yes you do need a work permit when you enter the country. However, if you and the company like each other, there is no (big) problem in the company organising a work permit for you. So you just leave to Ecuador for example, and come back on a work permit. But, getting the work permit is quite a hassle. You can stay on a tourist visa for a while and work under the table, see if you like it. And I can guarantee you'll love it in Medellin! =))